here's a rough breakdown(Taken from official wow forums)
Gnomish Engineering Only
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Lil' Smoky
World Enlarger
Gnomish Goggles
Gnomish Battle Chicken
Gnomish Death Ray
Gnomish Alarm-O-Bot
Ultrasafe Transporter - Gadgetzan
Goblin Engineering Only
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Pet Bombling
Goblin Construction Helmet
Goblin Mining Helmet (Mail)
Goblin Bomb Dispenser
Goblin Dragon Gun
Dimensional Ripper - Everlook
Next there are some items which can only be made by one engineering type however both can use the item. These are as follows.
Gnome Make, Goblin Useable
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Gnomish Net-o-Matic Projector
Gnomish Shrink Ray
Gnomish Harm Prevention Belt (Leather)
Gnomish Cloaking Device
Gnomish Rocket Boots
Gnomish Mind Control Cap
Goblin Make, Gnome Useable
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Goblin Sapper Charge (Consumable)
Goblin Mortar (Consumable, Goblin rechargeable)
Goblin Rocket Boots (Can be Destroyed)
The Big One (Consumable)
Goblin Jumper Cables XL (Can be Destroyed)
Goblin Rocket Helmet